from what i know, we can now fuck gunther, you just need to spend your free day at your bedroom taking care of some urges. if your bond with him is high enough, he'll appear and offer to help you out, and done! i dont know if it'll be you fucking him or him fucking you, but if you get the option where you bottom, on your next free day you can go to the backyard and ask him about "that offer..." , then you should be able to choose between top or bottom.
unfortunately we cant fuck terrance, but i sure do hope that we can!